Projection- type picture display apparatus and screen used thereby

ABSTRACT

A screen for allowing light generated by a light source and modulated by a picture display device having pixels laid out to form a matrix to produce an image thereon to be projected on the screen as an enlarged picture. The screen has a Fresnel lens sheet forming Fresnel lenses at an emission side, a first member for receiving light emitted from the Fresnel lens sheet having light passing windows, and a plurality of light absorbing layers and a second member placed on the emission side of the first member. A pitch of the light absorbing layers is made smaller than a pitch in a first direction of pixels projected and enlarged on the screen, and a pitch in a second direction of the pixels is at least twice of a pitch of the Fresnel lenses.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] In general, the present invention relates to a projection-typepicture display apparatus such as a projection television set and ascreen used thereby. More particularly, the present invention relates toa projection-type picture display apparatus which has a small amount ofinadvertent inclusion of external light, is capable of suppressing areduction in contrast and capable of lowering the degree ofdeterioration of a picture quality by using an optical device having astructure comprising pixels laid out to form a matrix such as aliquid-crystal panel or a DMD (Digital Micromirror Device) as a picturegenerating source, and relates to a screen used by the projection-typepicture display apparatus.

[0003] 2. Description of the Related Art

[0004] With the picture source going diverse, the projection-typepicture display apparatus is enjoying broad general popularity in themarket by virtue of its marketability factors of a projection-typeoptical apparatus with a large screen such as a small weight, a low costand a small size. On the other hand, in recent years, a projection-typepicture display apparatus using a liquid-crystal panel as a picturegenerating source starts its participation in the market due tosubstantial improvement of the precision/fineness and the numericalaperture of the liquid-crystal panel. This projection-type picturedisplay apparatus is designed into a configuration wherein a sourcepicture displayed on the liquid-crystal panel is displayed as anenlarged picture on a screen in full colors by a projection lens unit.

[0005] In an optical system employed in this projection-type picturedisplay apparatus, it is possible to adopt a three-panel techniqueemploying three liquid-crystal panels as shown in FIG. 19 of JapaneseUnexamined Patent Publication No. Hei9-96759, or a single-paneltechnique employing only one liquid-crystal panel as shown in FIG. 1 ofJapanese Unexamined Patent Publication No. Hei4-60538. First of all, anoptical system adopting a single-panel technique employing oneliquid-crystal panel is explained by referring to FIG. 1.

[0006]FIG. 1 is a top-view diagram showing a partial cross section of alayout of a projection-type optical system adopting a single-paneltechnique employing one liquid-crystal panel.

[0007] As shown in the figure, a reflective mirror 29 directs a beamemitted by a white-color light source 28 implemented by a metal halidelamp, a canon lamp, a halogen lamp or a high-pressure mercury lamp to aconverging lens 27 with a high degree of efficiency whereas a collimatorlens 26 converts the beam into all but parallel white-color lights.Three dichroic mirrors 23, 24 and 25 with types different from eachother are placed in front of the collimator lens 26. The dichroicmirrors 23, 24 and 25 exhibit characteristics to selectively reflectlights with the green, red and blue wavelengths respectively but to passon other components. Symbols R, G and B in the figure denoterespectively the red, green and blue lights split by the dichroicmirrors 24, 23 and 25. In this conventional configuration, the red-colorlight is taken as a reference while the blue-color and green-colorlights are radiated to a liquid-crystal panel 22 from slantingdirections relative to the red-color light.

[0008] The liquid-crystal panel 22 comprises pixels for the 3 primarycolors, namely, red, green and blue. The pixels each exhibit an opticaltransmittivity representing the level of a luminance component of apicture signal. Thus, the red, green and blue lights are modulated inaccordance with the level of the picture signal to create a desiredimage on the liquid-crystal panel 22. The image displayed on theliquid-crystal panel 22 is then projected by a projection-lens unit 21on a screen 20 as an enlarged picture.

[0009] In order to radiate an image light emitted by the liquid-crystalpanel 22 to the projection-lens unit 21 with a high degree ofefficiency, an optical system including a convex lens for converging alight is typically provided between the liquid-crystal panel 22 and theprojection-lens unit 21. It should be noted that such an optical systemis not shown in FIG. 1.

[0010] The white-color light source 28 itself dissipates heat which canbe a cause of a damage. On the other hand, the liquid-crystal panel 22including a polarizing plate absorbs an incident light, dissipating heatwhich can also be a cause of a damage. In order to reduce an increase intemperature, a cooling fan not shown in the figure is used to forciblycool the white-color light source 28 and the liquid-crystal panel 22 sothat they can be used at a temperature in a desired range.

[0011] Next, the optical system adopting the conventional three-paneltechnique, that is, employing three liquid-crystal panels, is explainedby referring to FIG. 2.

[0012]FIG. 2 is a top-view diagram showing a partial cross section of alayout of a projection-type optical system adopting the conventionalthree-panel technique employing three liquid-crystal panels.Configuration components shown in the figure identical with those of theoptical system shown in FIG. 1 are denoted by the same referencenumerals as those of the latter. The optical system shown in FIG. 2 hasa configuration wherein a reflective mirror 29 collimates a beam emittedby a white-color light source 28 implemented by a metal halide lamp, acanon lamp, a halogen lamp or a high-pressure mercury lamp into all butparallel white-color lights. Two dichroic mirrors 31 and 32 with typesdifferent from each other are placed in front of the reflective lens 29.The dichroic mirrors 31 and 32 split the beam into color componentswhich are then radiated to their respective liquid-crystal panels 33, 34and 35. Pictures displayed on the liquid-crystal panels 33, 34 and 35are synthesized by a color synthesizing prism 36 before being projectedby a projection-lens unit 21 on a screen 20 as an enlarged picture.Since the operation of the projection-type optical system adopting theconventional three-panel technique employing the three liquid-crystalpanels is the same as the conventional system shown in FIG. 1, it is notnecessary to repeat its explanation.

[0013] In addition, a forced cooling system of the white-color lightsource 28 and the liquid-crystal panels each including a polarizingplate is the same as the optical system shown in FIG. 1. Furthermore, aradiation system to increase the efficiency of light utilization hasbecome popular in recent years. The radiation system has apolarized-light synthesizing function for synthesizing P and S polarizedlights generated by a polarization beam splitter as a result ofsplitting of a light emitted by the light source.

[0014] A rear-projection-type picture display apparatus employing theoptical systems explained above is described by referring to FIGS. 3 and4.

[0015]FIGS. 3 and 4 are each a side-view diagram showing a partial crosssection of main components of the rear-projection-type picture displayapparatus employing the projection-type optical system. In the figures,reference numerals 11 and 12 denote a radiation system including a lightsource and a projection lens respectively. Reference numeral 13 denotesan optical-path reflection mirror and reference numeral 14 denotes ascreen. Reference numeral 15 denotes a case. The length of an opticalpath from the projection lens 12 to the screen 14 in therear-projection-type picture display apparatus shown in FIG. 3 is equalto that of the apparatus shown in FIG. 4. Since the rear-projection-typepicture display apparatus shown in FIG. 3 has a comparatively big depth,its height can be made relatively small. Since the rear-projection-typepicture display apparatus shown in FIG. 4 has a comparatively bigheight, on the other hand, its depth can be made relatively small. Ineither of the rear-projection-type picture display apparatuses, byshortening the projection distance of the projection lens 12, that is,the length of the optical path from the projection lens 12 to the screen14, a compact set can be implemented by employing only one optical-pathreflection mirror 13. As the screen 14, a screen 40 having a two-sheetstructure is normally employed. The screen 40 comprising a lenticularlens sheet and a Fresnel lens sheet is used in a projection-type picturedisplay apparatus employing a Braun tube 43 shown in FIG. 10.

[0016]FIG. 10 is a side-view diagram showing a partial cross section ofmain components of the rear-projection-type picture display apparatusemploying the projection-type Braun tube 43. It should be noted that, inthe figure, reference numerals 40 and 41 denote a screen and aprojection lens respectively whereas reference numerals 42 and 43 denotea bracket and a projection-type Braun tube respectively. Referencenumeral 44 denotes an optical path of a light projected from theprojection-type Braun tube 43 to the screen 40 provided at the end of aradiation path.

[0017] A detailed configuration of the screen 40 shown in FIG. 10 isshown in FIGS. 12 and 13.

[0018]FIGS. 12 and 13 are each a diagram showing a squint view of maincomponents of the conventional screen 40. Components of FIG. 12identical with those shown in FIG. 13 are denoted by the same referencenumerals as the latter. The screen 40 shown in FIG. 12 comprises aFresnel lens sheet 51 a and a lenticular lens sheet 52. On the otherhand, the screen 40 shown in FIG. 13 comprises a Fresnel lens sheet 51 band a lenticular lens sheet 52. The lenticular lens sheet 52 comprises alenticular lens 54 on the incidence surface, a lenticular sheet 56 onthe emission surface and a light absorbing layer 57 provided on aprotrusion 55. The Fresnel sheet 51 a has a flat incidence surface and aFresnel lens 53 on the emission surface thereof. On the other hand, theFresnel sheet 51 b comprises a lenticular lens 58 provided on theincidence surface thereof and a Fresnel lens 53 provided on the emissionsurface thereof. As described above, the screen 40 shown in FIG. 12 isdifferent from that shown in FIG. 13 in that, in the case of the former,no lenticular lens 58 is provided on the image-light incidence surfaceof the Fresnel sheet 51 while, in the case of the latter, the lenticularlens 58 is provided. It should be noted that the lenticular lens 58 hasits longitudinal direction coinciding with the horizontal direction ofthe screen 40.

[0019] In a screen having a two-layer structure comprising a lenticularlens sheet 52 and a Fresnel lens sheet 51 used in a rear-projection-typepicture display apparatus employing the conventional projection-typeBraun tube, the horizontal-direction width of the screen of the lightabsorbing layer 57 provided on the picture-viewing side of thelenticular lens sheet 52 can be made larger than the width of thelenticular lens 56 on the emission surface. That is, if the width of thelenticular lens 56 on the emission surface is made small, the efficiencyof the light utilization decreases. Thus, the width of the lightabsorbing layer 57 in the screen horizontal direction can not be madelarge. For this reason, there exists a phenomenon in which an externallight is reflected to the lenticular lens 56 provided on the emissionsurface. This phenomenon raises a first problem that remains to besolved. The problem is that the inadvertent inclusion of an externallight can not be reduced to a value below a predetermined amount and thedegree of contrast deterioration can not be suppressed below apredetermined level.

[0020] The following description explains in detail reasons why thefirst problem arises.

[0021]FIG. 11 is a diagram showing a top view of a layout of therear-projection-type picture display apparatus employing theconventional projection-type Braun tube on a horizontal plane in asimple and plain manner. As described above, the rear-projection-typepicture display apparatus employs the conventional projection-type Brauntube in the horizontal-plane layout.

[0022] In FIG. 11, reference numerals 7R, 7G and 7B denote red, greenand blue projection-type Braun tubes respectively whereas referencenumerals 8R, 8G and 8B denote projection lens associated with the red,green and blue projection-type Braun tubes 7R, 7G and 7B respectively.Reference numerals 10R, 10G and 10B denote red, green and blue projectedbeams respectively. In the optical system of the rear-projection-typepicture display apparatus, in actuality, there are reflective mirrorsfor reflecting the red, green and blue projected beams 10R, 10G and 10B.These reflective mirrors are omitted from FIG. 11. Reference numerals13R, 13G and 13B denote optical axes of the projection lenses 8R, 8G and8B respectively. The optical axes 13R, 13G and 13B cross each other,forming optical-axis convergence angles θ at a point S0 in closeproximity to the screen 40.

[0023] As shown in FIG. 11, the projected beams 10R, 10G and 10B areeach spreading before hitting the screen 40. Pay attention to a specificprojected beam, that is, the red projected beam 10R for example. Lightsof the red projected beam 10R emanating from the projection lens 8Rtoward pixels on the screen 40 are not parallel. Instead, those lightsare becoming more distant from the main light hitting the center pixelon the screen 40 or the optical axis 13R.

[0024] A light hitting a pixel on the screen 40 in the same direction asthe main light hitting the center pixel has the highest intensity amongthe lights reaching the pixels on the screen 40. That is, the directionof the main light is a direction of the highest intensity. Thus, to aviewer at a fixed position, only a portion of the picture is brightwhile surrounding portions are dark. This phenomenon is referred to as acolor shift. In order to reduce the effect of the color shift, in thescreen 40 shown in FIG. 12 or 13, a spread picture beam arriving at theincidence surface of the Fresnel lens sheet 51 is converted into analmost parallel beam passing through the Fresnel lens 53 and leaving forthe lenticular lens sheet 52 for each of the red, green and blue colors.

[0025]FIGS. 14 and 15 are each a diagram showing a partial enlargedcross section of the lenticular lens cut in a direction A-A1 shown inFIG. 13.

[0026] In these figures, reference numeral 54 denotes the lenticularlens provided on the surface of incidence of the picture light andreference numeral 56 denotes the lenticular lens provided on the surfaceof emission of the picture light.

[0027] According to a conventional technology disclosed in JapaneseUnexamined Patent Publication No. Sho58-59436, the lenticular lens 54provided on the incidence surface has a surface resembling a portion ofthe surface of an elliptical cylinder. The direction of the major axisof the ellipse coincides with the direction of a thickness between theincidence surface 54 and the emission surface 56 which is indicated bynotation 1-1′ in FIGS. 14 and 15. One of the two foci of the ellipse isplaced at an inner portion in close proximity to the lenticular lens 54provided on the incidence surface. The other focus is placed at aposition in close proximity to the lenticular lens 56 provided on theemission surface. The eccentricity e of the ellipse is set at a valueapproximately equal to the reciprocal of the refractive index n of thematerial of the lenticular lens sheet 52.

[0028] In such a configuration, all incident lights arriving at thelenticular lens 54 provided on the incidence surface in a directionparallel to the major axis of the ellipse are converged on the focus inclose proximity to the lenticular lens 56 provided on the emissionsurface and spread in screen surface horizontal directions from thisfocus.

[0029] As for the lenticular lens 56 provided on the emission surface,the shape of the emission surface resembles the surface of an ellipticalcylinder all but similar to the surface of an elliptical cylinder on theincidence-surface side. For an incident beam 60 at an edge shown in FIG.14, the lenticular lens 56 provided on the emission surface functions tomake the directional characteristic of the emitted light all butsymmetrical with respect to the optical axis indicated by notation 1-1′in the figure. Furthermore, for an incident beam 62 coming from aslanting direction of the red or blue color as shown in FIG. 15, thelenticular lens 56 provided on the emission surface has a correctingfunction to make the directional characteristic of the emitted light allbut symmetrical with respect to the optical axis indicated by notation1-1′ in the figure. In addition, the beam is not converged at a pointdue to frame aberration occurring at a location in close proximity tothe emission surface at that time. Instead, the beam is spread in screenhorizontal directions.

[0030] Inside the actual lenticular lens sheet 52, a scattering material58 such as glass bead exists as shown in FIGS. 12 and 13, causing thebeam to be actually further spread. Basically, however, the width of thelight absorbing layer 57 in the screen horizontal direction can not beincreased to a value greater than the width of the lenticular lens 56provided on the emission surface. As a result, the quantity of lightreflected due to inadvertent inclusion of an external light can not bereduced and a decrease in contrast can not be made lower than apredetermined value.

[0031] In addition, an incident beam 62 coming from the red or blueslanting direction is not converged at a point due to frame aberrationoccurring at a location in close proximity to the emission surface.Instead, the beam is spread in screen horizontal directions as describedabove. As a result, the width of the surface of the lenticular-lenssurface can not be reduced. Thus, in the case of the lenticular lenssheet 52 adopting the conventional technique employing the lenticularlenses 54 and 56 on both the incidence and emission surfaces, there israised a second problem that the lenticular-lens pitch in the screenhorizontal direction can not be reduced to a value smaller than 0.5 mm.

[0032] For the reason described above, the total focus performance(horizontal resolution) of the rear-projection-type picture displayapparatus is determined mainly by the lens pitch of the lenticular lens52 which has a performance inferior to that exhibited by theprojection-type Braun tube and the projection lens.

[0033] In addition, since the pitch of the lenticular lens 56 providedon the emission lens can not be reduced, a third problem is raised. Toput it in detail, when an optical device having a structure comprisingpixels laid out to form a matrix such as a liquid-crystal panel or a DMD(Digital Micromirror Device) is used as a picture generating source, thequality of a picture deteriorates due to moires generated on the entirescreen 40. The generation of such moires is attributed to three causes,namely, projected and enlarged pixels on the screen 40, the lenticularlenses 54 and 56 provided on the lenticular lens sheet 52 and theFresnel lens 53.

SUMMARY OF THE INVENTION

[0034] It is an object of the present invention addressing the problemsencountered in the conventional technology described above to provide ascreen and a projection-type display apparatus capable of reducinginadvertent inclusion of an external light and reducing a decrease incontrast when producing a projected and enlarged picture on the screenby using a projection lens from an image created by a picture generatingsource implemented by an optical device such as a liquid-crystal paneland a DMD (Digital Micromirror Device) with a structure comprisingpixels laid out to form a matrix.

[0035] It is another object of the present invention addressing theproblems encountered in the conventional technology described above toprovide a screen and a projection-type display apparatus capable ofreducing a decrease in picture quality caused by moires when producing aprojected and enlarged picture on the screen by using a projection lensfrom an image created by a picture generating source implemented by anoptical device such as a liquid-crystal panel and a DMD (DigitalMicromirror Device) with a structure comprising pixels laid out to forma matrix.

[0036] An optical system of the projection-type picture displayapparatus provided by the present invention employs an optical devicesuch as a liquid-crystal panel and a DMD (Digital Micromirror Device)with a structure comprising pixels laid out to form a matrix as apicture generating source besides one projection lens shown in FIGS. 1and 2. For this reason, since red and blue image lights are not radiatedin slanting directions with respect to the green image light, no frameaberration is generated on the screen.

[0037] As a result, since the width of a lenticular lens provided on theimage-light emission surface of a lenticular sheet can be reduced whilethe width of a light absorbing layer can be increased to a relativelylarge value, it is possible to reduce inadvertent inclusion of anexternal light and reduce a decrease in contrast.

[0038] A lens of provided on the incidence surface of the lenticularlens sheet is designed into a shape resembling the surface of anelliptical cylinder or a portion of a high-order non-spherical cylinder.When designed into the surface of an elliptical cylinder, the directionof the major axis of the ellipse coincides with the direction of thethickness between the incidence and emission surfaces. In addition, oneof the two foci of the ellipse is placed at a position in closeproximity to a lenticular lens provided on the incidence surface whereasthe other focus is placed at a position in close proximity to alenticular lens provided on the emission surface. In this case, theeccentricity e of the ellipse is set at a value approximately equal tothe reciprocal of the refractive index n of the material of thelenticular lens.

[0039] In such a configuration, incident lights hitting the lenticularlens on the incidence surface in a direction parallel to the major axisof the ellipse are all converged on the focus in close proximity to theemission surface and then spread from this focus in screen surfacehorizontal directions. For this reason, the width in the screenhorizontal direction of the lenticular lens provided on the emissionsurface can be reduced. In this case, the lens provided on the incidencesurface of the lenticular lens sheet can be designed into a shape of ahigh-order non-spherical surface in order to further increase theefficiency of the light convergence.

[0040] Because of the reasons described above, sincethe-screen-horizontal-direction width of the lenticular lens provided onthe emission surface can be reduced, the lens pitch of the lenticularlens can also be reduced as well. As a result, the total focusperformance (horizontal resolution) of the rear-projection-type picturedisplay apparatus using this screen can be improved.

[0041] In addition, in the screen provided by the present invention, thelens pitch of the lenticular lens can also be reduced as describedabove. Thus, even if the screen provided by the present invention isused in the projection-type picture display apparatus employing anoptical device having a structure comprising pixels laid out to form amatrix such as a liquid-crystal panel or a DMD (Digital MicromirrorDevice) as a picture generating source, moires generated on the entirescreen due to three causes are no longer striking. As described above,the three causes are projected and enlarged pixels on the screen, thelenticular lenses provided on the lenticular lens sheet and the Fresnellens.

[0042] The objects of the present invention can be achieved as follows.According to a first aspect of the present invention, there is provideda screen characterized in that, in order to allow a light generated by alight source and modulated by a picture display device comprising pixelslaid out to form a matrix to produce an image thereon to be projected byusing a projection optical means on the screen as an enlarged picture,the screen is provided with:a Fresnel lens sheet placed on an emissionside of the picture display device; a first configuration elementhaving: lenticular lenses provided on an incidence side of a lightpassing through the Fresnel lens sheet; and light absorbing layers eachprovided at a place in close proximity to the focal point of one of thelenticular lenses and are separated from each other by a predetermineddistance for forming the light passing unit; and a second configurationelement having a light passing plate fixed on the emission side of thefirst configuration element and a pitch of the light passing units ismade smaller than a pitch of pixels projected and enlarged on the screenfrom the image produced by the picture display device.

[0043] In the screen according to first aspect of the present invention,an emission surface of the light passing plate is subjected to areflection preventing process for preventing reflection of a visiblelight. As an alternative, on the emission side of the light passingplate, there can also be provided a reflection preventing film forpreventing reflection of a visible light.

[0044] In the screen according to the first aspect of the presentinvention, a light scattering material is mixed inside the light passingplate. As an alternative, a light scattering layer can also be providedbetween the light passing plate and the first configuration element.

[0045] In a screen according to the first aspect of the presentinvention, Fresnel lenses of the Fresnel lens sheet are laid out at apitch Fp; the light passing units are laid out in a horizontal directionof the screen at a pitch Lp; and

[0046] a ratio Lp/Fp of the pitch Lp to the pitch Fp is set at a valuein the range 1.588 to 1.649.

[0047] According to a second aspect of the present invention, there isprovided a screen for projecting an enlarged picture on the screen froma displayed picture output by a picture display apparatus comprising: alight source; a picture display device implemented as a matrix of pixelseach having a means for modulating the intensity of a light generated bythe light source; and a projection optical means for projecting thedisplayed picture appearing on the picture display device. The screen isprovided with: a first configuration element having a plurality oflenticular lenses provided on a light-emission side of the projectionoptical means and light absorbing layers provided on a light-emissionside of the first configuration element, and a light passing secondconfiguration element provided on the light-emission side of the firstconfiguration element. The lenticular lenses have a longitudinaldirection coinciding with a screen surface vertical direction and arelaid out contiguously in a screen surface horizontal direction; thelight absorbing layers are sandwiched by boundaries of any two adjacentopenings each provided at a location in close proximity to a focal pointof one of the lenticular lenses associated with the opening; the firstand second configuration elements are bound or stuck to each other; apitch of the openings is made smaller than a pitch of pixels projectedand enlarged on the screen from the displayed picture output by thepicture display device; and a pitch of interference lines caused by bothinterference sources is set at a value about equal to or smaller thanthe pitch of pixels projected and enlarged on the screen from thedisplayed picture output by the picture display device.

[0048] In the screen according to second aspect of the presentinvention, an emission surface of the light passing plate is subjectedto a reflection preventing process for preventing reflection of avisible light. As an alternative, on the emission side of the lightpassing plate, there can also be provided a reflection preventing filmfor preventing reflection of a visible light.

[0049] In the screen according to the second aspect of the presentinvention, a light scattering material is mixed inside the light passingplate. As an alternative, a light scattering layer can also be providedbetween the light passing plate and the first configuration element.

[0050] In the screen according to the second aspect of the presentinvention, a third configuration element having Fresnel lenses isprovided on a light-incidence side of the first configuration element;the Fresnel lenses of the third configuration element are laid out at alens pitch Fp; the openings of the first configuration element are laidout in a horizontal direction of the screen at a pitch Lp; a ratio Lp/Fpof the lens pitch Lp to the pitch Fp is set at a value in the range1.588 to 1.649; a pitch Mp1 of moire lines caused by both interferencesources is set at a value smaller than a pitch Iph of pixels projectedand enlarged on the screen in a screen horizontal direction from thedisplayed picture output by the picture display device; and a pitch ofinterference lines caused by the both interference sources is set at avalue about equal to or smaller than a pitch of pixels projected andenlarged on the screen from the displayed picture output by the picturedisplay device.

[0051] According to a third aspect of the present invention, there isprovided a projection-type picture display apparatus comprising:

[0052] a light source; a picture display device implemented as a matrixof pixels for modulating the intensity of a light generated by the lightsource; and a projection optical means for projecting a pictureappearing on the picture display device. A Fresnel lens sheet placed onan emission side of the picture display device; a first configurationelement having: lenticular lenses provided on an incidence side of alight passing through the Fresnel lens sheet; and light absorbinglayers; and a second configuration element having a light passing platefixed on the emission side of the first configuration element. The lightabsorbing layers are each provided at a place in close proximity to thefocal point of one of the lenticular lenses and are separated from eachother by a predetermined distance for forming the light passing unit;and a pitch of the light passing units is made smaller than a pitch ofpixels projected and enlarged on a screen from the picture generated bythe picture display device.

[0053] In a projection-type picture display apparatus according to thethird aspect of the present invention, on an emission side of the lightpassing plate, there is provided a reflection preventing film forpreventing reflection of a visible light.

[0054] In a projection-type picture display apparatus according to thirdaspect of the present invention, a light scattering material is mixedinside the light passing plate. As an alternative, a light scatteringlayer can also be provided between the light passing plate and the firstconfiguration element.

[0055] In a projection-type picture display apparatus according to thethird aspect of the present invention, Fresnel lenses of the Fresnellens sheet are laid out at a pitch Fp; the light passing units are laidout in a horizontal direction of the screen at a pitch Lp; and a ratioLp/Fp of the pitch Lp to the pitch Fp is set at a value in the range1.588 to 1.649.

[0056] According to a fourth aspect of the present invention, there isprovided a projection-type picture display apparatus comprising: a lightsource; a picture display device implemented as a matrix of pixels eachhaving a means for modulating the intensity of a light generated by thelight source; a projection optical means for projecting a displayedimage appearing on the picture display device; and a screen used by theprojection optical means to project the displayed image as an enlargepicture and provided with: a first configuration element having aplurality of lenticular lenses provided on a light-emission side of theprojection optical means and light absorbing layers provided on alight-emission side of the first configuration element, and a lightpassing second configuration element provided on the light-emission sideof the first configuration element. The lenticular lenses have alongitudinal direction coinciding with a screen surface verticaldirection and are laid out contiguously in a screen surface horizontaldirection; the light absorbing layers are sandwiched by boundaries ofany two adjacent openings each provided at a location in close proximityto a focal point of one of the lenticular lenses associated with theopening; the first and second configuration elements are fixed to eachother; a pitch of the openings is made smaller than a pitch of pixelsprojected and enlarged on the screen from the displayed image output bythe picture display device; and a pitch of interference lines caused byboth interference sources is set at a value about equal to or smallerthan the pitch of pixels projected and enlarged on the screen from thedisplayed image output by the picture display device.

[0057] In the projection-type picture display apparatus according to thefourth aspect of the present invention, an emission surface of thesecond configuration element is subjected to a reflection preventingprocess for preventing reflection of a visible light.

[0058] In the projection-type picture display apparatus according to thefourth aspect of the present invention, a light scattering material ismixed inside the second configuration element. As an alternative, alight scattering layer is provided between the second configurationelement and the first configuration element.

[0059] In the projection-type picture display apparatus according to thefourth aspect of the present invention, a third configuration elementhaving Fresnel lenses is provided on a light-incidence side of the firstconfiguration element; the Fresnel lenses of the third configurationelement are laid out at a lens pitch Fp; the openings of the firstconfiguration element are laid out in a horizontal direction of thescreen at a pitch Lp; a ratio Lp/Fp of the lens pitch Lp to the pitch Fpis set at a value in the range 1.588 to 1.649; a pitch Mp1 of moirelines caused by both interference sources is set at a value smaller thana pitch Iph of pixels projected and enlarged on the screen in a screenhorizontal direction from the displayed image output by the picturedisplay device; and a pitch of interference lines caused by the bothinterference sources_is set at a value about equal to or smaller than apitch of pixels projected and enlarged on the screen by the picturedisplay device.

[0060] These and other objects, features and advantages of the presentinvention will be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061]FIG. 1 is a top-view diagram showing a partial cross section of alayout of a projection-type optical system adopting the conventionalsingle-panel technique employing one liquid-crystal panel;

[0062]FIG. 2 is a top-view diagram showing a partial cross section of alayout of a projection-type optical system adopting the conventionalthree-panel technique employing three liquid-crystal panels;

[0063]FIG. 3 is a side-view diagram showing a partial cross section ofmain components of a rear-projection-type picture display apparatusemploying a projection-type optical system;

[0064]FIG. 4 is a side-view diagram showing a partial cross section ofmain components of another rear-projection-type picture displayapparatus employing a projection-type optical system;

[0065]FIG. 5 is a diagram showing a squint view of main componentsemployed in a screen implemented by a first embodiment of the presentinvention;

[0066]FIG. 6 is a diagram showing a squint view of a screen implementedby a second embodiment of the present invention which corresponds to across section B-B1 shown in FIG. 5;

[0067]FIG. 7 is a diagram showing a squint view of a screen implementedby a third embodiment of the present invention which corresponds to thecross section B-B1 shown in FIG. 5;

[0068]FIG. 8 is a diagram showing a top view of a lenticular-lens screento explain a relation between enlarged pixels obtained as a result orprojection and enlargement of a picture on a screen used in conjunctionwith a three-panel technique employing three liquid-crystal panels andthe screen itself;

[0069]FIG. 9 is a diagram showing a top view of a lenticular-lens screento explain a relation between enlarged pixels obtained as a result orprojection and enlargement of a picture on the screen used inconjunction with a single panel technique employing one liquid-crystalpanel and the screen itself;

[0070]FIG. 10 is a side-view diagram showing a partial cross section ofmain components of a rear-projection-type picture display apparatusemploying a projection-type Braun tube;

[0071]FIG. 11 is a diagram showing a top view of a layout of therear-projection-type picture display apparatus employing aprojection-type Braun tube on a horizontal plane in a simple and plainmanner;

[0072]FIG. 12 is a diagram showing a squint view of main components of aconventional screen;

[0073]FIG. 13 is a diagram showing a squint view of main components ofanother conventional screen;

[0074]FIG. 14 is a diagram showing a partial enlarged cross section of alenticular lens cut in a direction A-A1 shown in FIG. 13; and

[0075]FIG. 15 is a diagram showing a partial enlarged cross section of alenticular lens cut in a direction A-A1 shown in FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076] Some preferred embodiments of the present invention are describedby referring to diagrams as follows.

[0077]FIG. 5 is a diagram showing a squint view of main componentsemployed in a screen implemented by a first embodiment of the presentinvention. In the figure, reference numerals 77 and 76 denote a screenand a Fresnel lens sheet (a third configuration element) respectivelywhereas reference numeral 75 denotes a lenticular lens sheet. TheFresnel lens sheet 76 and lenticular lens sheet 75 are joined to eachother at their edges which are not shown in the figure. The basicmaterials of the Fresnel lens sheet 76 and lenticular lens sheet 75 areboth an all but transparent thermoplastic resin material. Referencenumeral 79 denotes the surface of incidence of an image light of theFresnel lens sheet 76. The screen implemented by this embodiment has ashape wherein lenticular lenses 80 with the longitudinal directionthereof coinciding with the screen surface horizontal direction are laidout contiguously in the screen vertical direction. A Fresnel convex lens78 is provided on the surface of emission of the image light. TheFresnel convex lens 78 is created by a compression formation technique.As an alternative, the Fresnel convex lens 78 can also be created at amuch lower cost by stacking layers of UV resin on a thermoplastic resinbase material. In addition, in the case of the Fresnel convex lens 78made of UV resin, only one die serving as a master is required. Even ifthe pitch of the Fresnel convex lens 78 is made finer, there will be noincrease in cost. Thus, practically, fine fabrication resulting in apitch in the range 120 microns to 60 microns is possible. Referencenumeral 74 denotes a lenticular lens provided on the incidence surfaceof a first configuration element 73 in a configuration wherein thelenticular lenses 74 with the longitudinal direction thereof coincidingwith the screen surface vertical direction are laid out contiguously inthe screen horizontal direction. A light passing window 81 for lettingan image beam pass through is provided at a location in close proximityto the focus of each of the lenticular lenses 74. In addition, a lightabsorbing layer 72 is provided between any adjacent two of the lightpassing windows 81 to prevent the contrast performance fromdeteriorating due to an effect of an external light. In this embodiment,the lenticular lenses 74 are provided on the incidence surface of thefirst configuration element 73 whereas the light passing windows 81 andthe light absorbing layers 72 are provided on the emission surface ofthe first configuration element 73. A second configuration element 71 isimplemented by a light passing plate 91.

[0078] By the way, the optical-axis-direction thickness of the firstconfiguration element 73 is about 1.5 times the lens pitch in the caseof an elliptical lens shape. Even if a non-spherical surface is used andthe focal point is shifted, the thickness is about 5 times the lenspitch. For this reason, if the lens pitch is reduced, the thickness isalso decreased, resulting in a small strength. In order to solve thisproblem, in this embodiment, the first configuration element 73 is boundor stuck to the second configuration element 71 to give a strength thatdoes not cause a problem in the practical use. It should be noted that,from the cost point of view, the second configuration element 71 isnormally made of thermoplastic resin. In the case of a screen with adiagonal of 50 inches, a thickness of at least 1 inch gives a strengththat does not cause a problem in the practical use. In this case, an airboundary surface between the first configuration element 73 and a secondconfiguration element 71 disappears, allowing the reduction in contrastdue to an unnecessary reflected light to be reduced. The screen can bemade better by providing a reflection preventing film 70 on theobservation-side surface of the second configuration element 71. In sucha configuration, the degree of deterioration of the picture quality dueto reflection of an external light can be lowered. For example, if forexample a special low-reflection film made by NIPPON OIL AND FATS CO.,LTD. (product name:ReaLook) is used as the reflection preventing film 70bound or stick to the observation-side surface of the secondconfiguration element 71, in the visible wavelength region, thereflectance is reduced to a value not exceeding 1%. As a result, it ispossible to substantially lower the degree of deterioration of thepicture quality due to inadvertent inclusion of an external light.

[0079] The embodiment implementing a screen provided by the presentinvention has been described so far. It should be noted that the surfaceof incidence of an image light of the Fresnel lens sheet 76 can befabricated into a plane surface or a mat surface. As an alternative, theincidence surface can be subjected to another fabrication technique.

[0080]FIG. 6 is a diagram showing a squint view of a screen implementedby a second embodiment of the present invention which corresponds to across section B-B1 shown in FIG. 5 and FIG. 7 is a diagram showing asquint view of a screen implemented by a third embodiment of the presentinvention which corresponds to the cross section B-B1. Components of thescreens of FIGS. 5, 6 and 7 denoted by the same reference numeral areidentical components.

[0081] In the screen shown in FIG. 6, an image light 81 entering thesurface 79 on the image-source side (or the incidence surface 79) of theFresnel lens sheet 76 is converted into all but parallel lights by thelens effect of the Fresnel convex lens 78. The parallel lights then hitthe lenticular lens 74 provided on the incidence light of the lenticularlens sheet 75. Then, due to the lens effect of the lenticular lens 74,the lights pass through the light passing windows 81 instead of enteringthe light absorbing layers 72. A scattering layer 89 including ascattering material 82 is provided between the first configurationelement 73 and the second configuration element 71. The scattering layer89 is bound or stuck firmly to the first configuration element 73 andthe second configuration element 71. The scattering layer 89 contributesto some of scattering of the image beam in the vertical and horizontaldirections of the screen. The image beam scattered by the scatteringlayer 89 travels through the second configuration element 71 toward theobservation side and then passes through the reflection preventing film70 before being emitted to the observation side.

[0082] In the embodiment shown in FIG. 7, the scattering layer 89 shownin FIG. 6 is not employed. The embodiment shown in FIG. 7 has the sameconfiguration as that of FIG. 6 except that a scattering material 82 isintroduced in the second configuration element 71 over the entiresurface of the light passing plate 91.

[0083] By configuring the screen 77 as described above, it is possibleto substantially reduce the deterioration in picture quality due toinadvertent inclusion of an external light. In addition, even if thepitch of the lenticular lens 74 employed in the first configurationelement 73 is reduced, the strength of the screen can be sustained at asufficient value. The screen can thus adopt fine pitches. As a result,the possibility of the horizontal resolution's becoming poorer islowered.

[0084] Next, a means for solving the moire problem is explained.

[0085] The following description explains a technology for reducingmoires which are generated in a case where an optical device having amatrix structure is employed in the optical system of theprojection-type picture display apparatus as a picture generatingsource. It is needless to say that the technology exhibits the sameeffect for other devices such as the digital micromirror device used asa picture generating source.

[0086]FIG. 8 is a diagram showing a top view of a lenticular-lens screento explain a relation between enlarged pixels obtained as a result orprojection and enlargement of a picture on the screen used inconjunction with a three-panel technique employing three liquid-crystalpanels and the screen itself. In order to make the description simple,the explanation of the Fresnel lens is omitted.

[0087] In actuality, there is no case in which pixels on any one of thethree liquid-crystal panels all overlap those on the other panels. Alsoin order to make the description simple, however, pixels on any one ofthe three liquid-crystal panels are assumed to all overlap those on theother panels.

[0088] Reference numeral 72 denotes a light absorbing layer provided onthe first configuration element 73 employed in the lenticular sheetwhich is shown by a line. Reference numeral 83 denotes theliquid-crystal panel's light shielding area hatched with slanting lines.Reference numeral 84 denotes the liquid-crystal panel's pixel (aneffective area) not hatched with slanting lines. The drawing as well asthe explanation of the Fresnel lens are omitted.

[0089] The historical development of the screen is long. A technique toreduce moires generated by the Fresnel and lenticular lenses isdisclosed in Japanese Examined Patent Publication No. Hei3-72972.According to this conventional technique, the ratio of the pitch Lp ofthe lenticular lens to the pitch Fp of the Fresnel lens is set at thefollowing value:

Lp/Fp=N+α

[0090] where the symbol N denotes a natural number in the range 1 to 12and the symbol a denotes a constant having a value in the range 0.35 to0.43.

[0091] In addition, according to Japanese Examined Patent PublicationNo. Hei5-63781,

[0092] Lp/Fp=5.525 to 5.682 or 6.472 to 6.645

[0093] Furthermore, in Japanese Examined Patent Publication No.Hei7-117818, the following ratio is disclosed:

Lp/Fp=N+0.5

[0094] where the symbol N is a natural number.

[0095] However, these technologies are developed for a case in which aBraun tube is used as a picture displaying source. For an optical devicehaving a structure comprising pixels laid out to form a matrix, none aredisclosed.

[0096] In the embodiment shown in FIG. 8, the vertical and horizontaldimensions of a liquid-crystal pixel are denoted by notations H and Wrespectively whereas the vertical and horizontal dimensions of aneffective area of the liquid-crystal pixel are denoted by notations HAand WA respectively. Let Iph and Ipv denote the pixel pitch in thehorizontal direction and the pixel pitch in the vertical directionrespectively whereas Fp and Lp respectively denote the pitch of theFresnel lens 76 shown in FIGS. 6 and 7 and the pitch of the lightabsorbing layer 72, that is the light passing window 81 provided on thefirst configuration element 73 employed in the lenticular lens sheet 75as shown in FIGS. 6 and 7. A moire pitch caused by the pitch Lp of thelight absorbing layer 72 and the pitch Fp of the Fresnel lens 78 isdenoted by notation Mp1 or, to be more specific, Mp1 h in the horizontaldirection and Mp1 v in the vertical direction. On the other hand, amoire pitch caused by the pitch Lp and the pitch Ip (with the pitchesIph and Ipv in horizontal and vertical directions respectively takeninto consideration) of an enlarged pixel is denoted by notation Mp2 or,to be more specific, Mp2 h in the horizontal direction and Mp2 v in thevertical direction. A moire pitch caused by the pitches Mp1 and Ip isdenoted by notation Mp3 or, to be more specific, Mp3 h in the horizontaldirection and Mp3 v in the vertical direction. First of all, a rangewith few generated moires was found by computation. In the case of theactual apparatus, an optimum condition was found with a projection sizeor the projection magnification of the pixel used as a parameter on thebasis of a Fresnel lens sheet with a fine pitch and a lenticular sheetwith a fine pitch which can be obtained at the present point of time,and a prototype was then built for verification purposes.

[0097] A moire frequency Fm (k, 1) expressed in terms of cycles/mm wascomputed by using the following approximation formula.

Fm(k, 1)=k/Fp−1/Lp

[0098] where notation k denotes the Fresnel harmonic order.

[0099] In this case, a positive polarity of Fm indicates generatedelliptical moires whereas a negative polarity of Fm indicates generatedhyperbolic moires.

[0100] Data of an optical system completing a verification experiment isgiven as follows. TABLE 1 (Item) (Performance) Lenticular lens sheetPitch 0.155 mm Fresnel lens sheet Parameter Conjugate point (52.5-inchprojection)   690 mm (40.3-inch projection)   530 mm Projected-pixelhorizontal-direction pitch:  1.334 mm (52.5-inch projection)Projected-pixel horizontal-direction pitch:  1.024 mm (40.3-inchprojection) Projected-pixel vertical-direction pitch: 1.0005 mm(52.5-inch projection) Projected-pixel vertical-direction pitch:  0.768mm (40.3-inch projection) Pixel count (dot) 800 (horizontal) 600(vertical) Projection lens F value 1.5 Half picture angle 44 degrees

[0101] Moires generated in the horizontal direction were calculated andevaluated for a 40.3-inch projection. The moire pitch Mp1 h caused bythe pitch Lp of the light absorbing layer 72 and the pitch Fp of theFresnel lens 78 was changed over the range 1.55 to 1.65 with the pitchFp of the Fresnel lens 78 taken as a parameter and evaluation was madeat intervals of 0.025. The results of the calculation and the evaluationset the moire pitch Mp3 h caused by the pitch Mp1 h and the pixel Iph inthe horizontal direction at a value of about 1.02 mm for a 40.3-inchprojection. The value of 1.02 mm is about equal to the pixel pitch Iphin the horizontal direction on the screen. This combination was verifiedby using an actual machine to find out that almost no moires weregenerated to cause a problem in the practical use such as substantialdeterioration of the picture quality. At that time, if the moire pitchMp1 h caused by the pitch Lp of the light absorbing layer 72 and thepitch Fp of the Fresnel lens 78 had a value in the range 1.575 to 1.625,the fact that a good performance was obtained was confirmed by using theactual machine. At that time, values of the Fresnel pitch were 0.0984mm, 0.0969 mm and 0.0954 mm. In addition, since the ratio (Ipv/Fp) ofthe pixel pitch Ipv in the vertical direction to the pitch Fp of theFresnel lens is close to 4, almost no moires were recognized by virtueof an optical scattering effect of the scattering layer 89 employed inthe lenticular lens sheet 75.

[0102] By the same token, moires generated in the horizontal directionwere calculated and evaluated for a 52.5-inch projection. The moirepitch Mp1 h caused by the pitch Lp of the light absorbing layer 72 andthe pitch Fp of the Fresnel lens 78 was changed, being set at values of1.55, 1.558, 1.600 and 1.649 with the pitch Fp of the Fresnel lens 78taken as a parameter, and evaluation was made. The results of thecalculation and the evaluation set the moire pitch Mp3 h caused by thepitch Mp1 h and the pixel Iph in the horizontal direction at a value ofabout 1.334 mm for a 52.5-inch projection. The value of 1.334 mm isabout equal to the pixel pitch Iph in the horizontal direction on thescreen. This combination was verified by using an actual machine to findout that almost no moires were generated to cause a problem in thepractical use such as substantial deterioration of the picture quality.At that time, if the moire pitch Mp1 h caused by the pitch Lp of thelight absorbing layer 72 and the pitch Fp of the Fresnel lens 78 had avalue in the range 1.558 to 1.649, the fact that a good performance wasobtained was confirmed by using the actual machine. At that time, theFresnel pitch was 0.0995 mm, 0.0969 mm and 0.0940 mm. In addition, sincethe ratio (Ipv/Fp) of the pixel pitch Ipv in the vertical direction tothe pitch Fp of the Fresnel lens is close to 4, almost no moires wererecognized by virtue of an optical scattering effect of the scatteringlayer 89 (the second configuration element 71 with the scatteringmaterial 82 mixed therein) employed in the lenticular lens sheet 75.

[0103] As described above, it is necessary to reduce moires generated bythe horizontal-direction component Iph and the vertical-directioncomponent Ipv of the pitch Ip of enlarged pixels, the pitch of thelenticular lens 74 and the pitch Fp of the Fresnel lens 78. This isbecause such moires cause the picture quality to deterioratesubstantially over the entire projection area of the screen when asource picture appearing on a device comprising pixels laid out to forma matrix is projected on the screen as an enlarged picture by using aprojection lens. In order to reduce such moires it is thus necessary toset the ratio (Lp/Fp) of the pitch Lp of the light absorbing layer 72provided on the first configuration element 73 employed in thelenticular lens sheet 75 to the pitch Fp of the Fresnel lens 78 at avalue of about 1.6, as well as to set the moire pitch Mp1 caused by thepitches Lp and Fp at a value about equal to the horizontal component Iphof the pitch Ip. In addition, it also necessary to set the ratio(Ipv/Fp) the vertical-direction component Ipv of the of the pixel pitchIp of enlarged pixels to the pitch Fp of the Fresnel lens at a value ofat least two.

[0104] Then, the same evaluation was made with the pitch of the Fresnellens 78 set at 60 microns to verify by using an actual machine that amore excellent performance not recognizing moires of even higher orderscould be obtained.

[0105] The above description explains a case in which a picture isprojected and enlarged on a screen by using an optical device adoptingthe three-panel technique utilizing three liquid-crystal panels. In thecase of a single-panel system using only one liquid-crystal panel likethe one shown in FIG. 9, it has been confirmed by using an actualmachine that a pixel-trio pitch can be treated to be the same as thepixel pitch of the three-panel technique described above. The pixel-triopitch is a pitch with 3 pixels treated as a set.

[0106]FIG. 9 is a diagram showing a top view of a lenticular-lens screento explain a relation between enlarged pixels obtained as a result orprojection and enlargement of a picture on the screen used inconjunction with a single panel technique employing one liquid-crystalpanel and the screen itself. In the figure, reference numeral 72 denotesa light absorbing layer whereas reference numerals 85, 86 and 87 eachdenote a pixel. The symbol d denotes the width of a blocked-light areaof the liquid-crystal panel and the symbol D denotes the width of aneffective area of the liquid-crystal panel.

[0107] By employing a screen with a configuration described above in aprojection-type picture display apparatus for projecting an imageappearing on an optical device such as a liquid-crystal panel or a DMD(Digital Micromirror Device) with a structure comprising pixels laid outto form a matrix on the screen as an enlarged picture by using aprojection lens, inadvertent inclusion of an external light can bereduced so that the contrast deterioration can be decreased and, at thesame time, the resolution degradation can be made smaller while thedeterioration of the picture quality can also be lessened so that, as aresult, it is possible to implement a good performance.

[0108] The present invention may be embodied in other specific formswithout departing from the spirit or essential characteristics thereof.The present embodiments are therefore to be considered in all respectsas illustrative and not restrictive. That is, the scope of the presentinvention is indicated by the appended claims rather than by theforegoing description. In addition, all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein.

What is claimed is:
 1. A screen for allowing light generated by a lightsource and modulated by a picture display device having pixels laid outto form a matrix to produce an image thereon to be projected on saidscreen as an enlarged picture, said screen comprising: a Fresnel lenssheet forming Fresnel lenses at an emission side of said light; a firstmember disposed for receiving light emitted from said Fresnel lens sheetand having light passing windows formed at a light emission side of saidfirst member, and a plurality of light absorbing layers each providedamong said light passing windows; and a second member placed on saidemission side of said first member and adhered to said first member;wherein a pitch of said absorbing layers formed on said first member ismade smaller than a pitch in a first direction of pixels projected andenlarged on said screen from said image produced by said picture displaydevice, and a pitch in a second direction of the pixels projected andenlarged on said screen from said image produced by said picture displaydevice is at least twice of a pitch of said Fresnel lenses formed onsaid Fresnel lens sheet, the second direction being transverse to thefirst direction.
 2. A screen according to claim 1, wherein the firstdirection is a horizontal direction and the second direction is avertical direction.
 3. A screen according to claim 1, wherein the firstmember includes lenticular lenses.
 4. A screen according to claim 1,wherein the lenticular lenses are disposed at a light incidence side ofthe first member.
 5. A screen according to claim 1, wherein the firstmember enables spreading of the light emitted from the Fresnel lenssheet at the emission side thereof.